Easy and Efficient CSO Monitoring through a Flap Gate

Written by Alain Charron, Cynthia Wiebe, Jean-Philippe Laliberté

WEFTEC, September 29 – October 3, 2012

This paper presents an investigation verifying the ability to estimate CSO volume based on the measurements of the inclination of a flap gate and flow depths at CSO outfalls.

As part of the City of Winnipeg CSO Monitoring Program, the use of an inclinometer coupled with level sensors has already been proven to be reliable in detecting overflows. Moreover, this set-up can constitute a monitoring system capable of estimating the quantity of discharge when an overflow occurs. Relationships for the outfall flow rate involving the gate inclination, upstream and downstream flow depths and some of the physical characteristics of the pipe and gate are proposed. It is based on the deterministic equation of the orifice relationship adapted to estimate the area of flow through the flap gate opening. Compared to flow data, the relationship provides interesting results confirming the applicability and the feasibility of flow monitoring through a flap gate for different gate sizes, various hydraulic conditions in pipes, and various ranges in flow depth. As such, this monitoring approach can be an interesting cost-effective alternative to the use of a flow meter in an outfall where flow conditions are in general not favourable for accurate and reliable velocity readings and where maintenance is frequently an issue.

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